ESR and resonance Raman spectroscopic studies of peroxide intermediates derived from iron diazaoxacyclononane

A peroxide-Fe3+ intermediate generation during the Fenton reaction of iron chelate involving a ligating N,N'-di-2-picolyl-4, 7-diaza-1-oxacyclononane (DPC), H2O2/[Fe2+ DPC]2+, is reported. The identity of this peroxide complex is confirmed by resonance Raman (RR) and electron spin resonance (ESR) spectroscopies. The RR spectrum of [Fe2+ DPC]2+ treated with H2O2 shows a frequency at 854 cm(-1) ascribable to v(O-O) vibrational modes of the peroxide-Fe3+ complex with a side-on geometry. On the other hand, the ESR spectrum of H2O2/[Fe2+ DPC]2+ acquired at 77 K exhibits the resonance transition at g = 2.196 and 2.017 due to the peroxide-Fe3+ complex with an axial symmetry. It has been concluded that the H2O2/[Fe2+ DPC]2+ reaction proceeds by rapid bonding of H2O2 to an open coordination site on the central Fe2+ cation.